Proper application of a thin layer of a substance such as a lubricant or protective film onto a substrate is generally one of the most critical considerations in processes involving the manufacture of items such as magnetic hard discs, semiconductor devices, circuit boards, flat panels such as liquid crystal displays, optical components such as mirrors, lenses, gratings and optical filters, etc. The coating layer must often have a precise and uniform thickness or the functional characteristics of the substrate are adversely affected. Moreover, the coating may have a thickness requirement that is so thin as to be difficult to obtain using generally known processes.
Often times available processes envision coating of both sides of a substrate, coating on only one side being impractical in view of the process. One process used for applying coating to one side of a substrate is called spin coating. In this process a substrate is spun about a rotation axis and a mixture of solvent and the coating material is poured onto the spinning substrate. The thickness of the coating is controlled by controlling the angular velocity of the spinning substrate and the viscosity of the mixture of solvent and coating material. Coatings applied with the spin process are often difficult to control in thickness and generally result in a greater thickness near the outer edges of the spinning substrate.
A process for providing coating thicknesses under one thousand Angstroms together with an apparatus for performing such processes to one side only of a substrate is needed throughout those industries that require ultra thin and precise coating applications.